Error found:
in module Main
at tests/purs/failing/2542.purs:8:16 - 8:17 (line 8, column 16 - line 8, column 17)

  Type variable a is undefined.

while inferring the kind of a
while checking that type a
  has kind Type
while inferring the kind of Array a
while checking that expression bar       
                                 where   
                                 bar = []
  has type Array a0
in value declaration foo

where a0 is a rigid type variable
        bound at (line 7, column 7 - line 7, column 10)

See https://github.com/purescript/documentation/blob/master/errors/UndefinedTypeVariable.md for more information,
or to contribute content related to this error.